In many electrical applications, uninterrupted power free from transient currents, voltages, and other forms of electrical noise are required. Those undesirable pulses and noise may be generated by outside disturbances such as lightning, motor generators, electrically driven devices etc., which originate within a facility from other loads interacting with each other or interconnected via the electrical distribution or data cables. There is thus a need for suppression of unwanted electrical noise and isolating transient pulses from any external power source. Additionally, there are fault voltages which may be generated within an electrical device. For example, in computer systems, a large majority of data loss or system problems result from poor grounding of power supplies. These problems are compounded with increased gate densities on integrated circuits.
Electrical contamination of only half a volt may cause data errors in present computer systems. With digital logic referencing ground at all times, it is imperative that a zero reference free of transient voltages or currents or noise be provided on the ground plane. Electrical impulses of greater magnitude are even more damaging because they may degrade a computer system's performance by eating away at the silicon underlying integrated circuits causing pitting on the surface. This in turn eventually degrades or destroys integrated circuit operation leading to complete data and system loss.
A typical grounding system has multiple functions which include personnel safety, serving as a steady zero electronic volt reference, lightning protection and a path for fault current. There are several established standards for proper grounding and proper alternating current (AC) distribution. Those include UL, ANSI C62.41, and IEEE 587 standards and National Electrical Codes, all of which must be met for normal applications. Additionally per UL, power isolators must have a practical limit to withstand at least 6000 volts to compensate for conductor spacing of typical electrical wiring systems. Traditionally, surge suppressors have been used to nullify (limit) transient voltages. Unfortunately such devices convert surge voltages to undesirable surge currents on the system data ground.
One method of eliminating unwanted transient voltages uses an isolated power supply. Typically this is accomplished by an isolation transformer. The transformer's primary windings are connected to an external alternating current (AC) voltage source. The electrical load sought to be protected is connected to the secondary windings and thus is electrically isolated from the AC voltage source and any transients from the external source. Although this arrangement eliminates some transients other current and voltage surges such as ground fault current may still occur in the secondary winding and thus be passed to the load. Additionally, as the primary and secondary grounds are electrically tied to the same "ground plane," there is no way to stop unwanted noise from choosing any path it wishes to the "protected" load on the secondary winding or to the primary winding.
Another method of shunting transient pulses involves tying an impedance to the primary ground input of a transformer. In this configuration both the primary and secondary windings of the transformer have a source (line power), neutral and ground tap. The secondary ground tap is connected to the primary ground tap and is tied to an external ground through the impedance. The impedance thus shunts transient high frequency current away from the input voltage lines of the electrical load connected to the secondary windings but allows 60 Hz AC voltage to pass through the transformer windings. The impedance is typically a toroid having a number of windings around a cylindrical core.
The toroid's maximum impedance is limited due to the diameter of the core. Additionally, the wire thickness necessary for high frequency applications limits the number of turns on the toroid. Coupling the toroid on the transformer's primary windings leaves a potential difference between the earth ground, chassis ground, isolated ground and the neutral ground of the load. Thus, because of the toroid's size, UL regulations limit the isolating power source using this method to 5 amps. Additionally, UL regulations require double insulation, such as a layer of heat shrink, air space and/or electrical insulating paper, on all the wires of the isolator device, isolator components, and the load itself for safety reasons. Such requirements for isolator devices are understandably difficult to meet and limit performance. In addition, external ground wires must be tied to the earth ground or isolated ground if not double insulated. Thus, isolated grounds with this type of deices still presents a challenge to maintaining the zero reference for high current, high voltage loads.
Accordingly there is a need for an isolated power supply that provides a true ground free from a wide range of transient voltages, currents and high frequency interference. There is also a need for a power isolator which meets safety standards for larger power sources over 5 amps. Additionally, there is a need for a power isolator which does not require double insulation on all electrical surfaces or connected loads.